1. Technical Field
The present invention relates generally to ophthalmic aids and procedures for correcting double vision or "diplopia" and, more particularly, to apparatus and methods of treating monocular or binocular diplopia by partial occlusion of vision.
2. Background Art
"Diplopia" is a disorder of vision which causes objects to appear double. When diplopia originates from a single eye, it is referred to as "monocular diplopia." A more common disorder is "binocular diplopia," which results from an imbalance in the muscles that move both eyes. The present invention encompasses embodiments for treating both types of diplopia.
Monocular diplopia is extremely rare and usually indicates a functional problem with the eye which produces a refractive error. Binocular diplopia occurs when both eyes do not move together in a coordinated manner. In such case, each eye is not seeing the same thing at the same time.
As explained in an article entitled: "Differential Diagnosis of Vision Loss," written by Jean E. Holt, M.D. and John B. Selhorst, M.D., published in "Patient Care", dated Jan. 30, 1987 (p. 62), diplopia can result from head trauma or a serious underlining disorder, such as a nerve palsy of the external eye muscles. Diseases that cause nerve palsy and the resulting imbalance of the eye muscles include multiple sclerosis, diabetes, thyroid disease, and myasthenia gravis. Diplopia may also result, for example, from aneurysms, brain tumors, head trauma, and meningitis.
Multiple Sclerosis (MS) patients are frequent sufferers of binocular diplopia. A prominent neurologist, John K. Wolf, M.D., from the Department of Neurology, at the State University of New York, Health Science Center, Syracuse, New York, has explained how diplopia is caused in MS patients, in his book entitled "Mastering Multiple Sclerosis" (2nd Ed.), page 315. Dr. Wolf teaches that a small tract in the brain stem coordinates movements of the eyes when looking to the left or to the right. This region of the brain stem often accumulates MS plaques, which interrupts coordinated movements of the eyes, and prevents the eyes from turning precisely together. The result is that the MS sufferer sees a double image.
Aside from treating the underlining cause of diplopia, doctors have had (to applicant's knowledge) only two devices at their disposal to treat its symptoms. These devices are an eye patch and Fresnel prisms. The eye patch is used in treating monocular diplopia by simply covering the affected eye. With binocular diplopia, the eye patch covers one eye, and thus eliminates one of the images received in the brain. Fresnel prisms operate to refract images received from one or both eyes.
The eye patch has certain obvious drawbacks, in that it blocks all vision from an eye that still has important sight capability. For example, peripheral vision from the patched eye is lost. In addition, the ability to look to the side on which the covered eye is located ("side vision"), is substantially impaired, because vision is established only from the eye located on the other side. Such loss of side vision is unnecessary, particularly in the case of binocular diplopia, as will become apparent from reading the description of the present invention hereinbelow. Another drawback with the eye patch is that it is cosmetically unacceptable to many individuals.
As for Fresnel prisms, it is applicant's understanding that such devices are not suitable in cases where the symptoms of diplopia are constantly changing. This is the usual case for MS sufferers, where vision is affected by heat, lighting, illness, fatigue and emotional state. Accordingly, the application of Fresnel prisms are limited. Another drawback with Fresnel prisms is that, they too are perceived by many as cosmetically desirable.